1. Field of Invention
The present invention relates to torsion damping devices, such as those which are for example incorporated in friction clutches for motor vehicles.
2. Description of the Prior Art
Friction clutches are known which are equipped with a torsion damping device comprising two torsion dampers: a main damper, or first damper, and a pre-damper, or second damper.
The first damper includes an input element which is fixed to two guide rings disposed on either side of a damper plate. The guide rings are coupled together by means of spacers which secure them together. The input element consists, in the case of application to a friction clutch, of a support disc, on each of the faces of which there are fixed friction liners that are adapted to be gripped between the pressure and reaction plates of the clutch.
In another version, the input element may consist of a disc which is fixed directly on an engine flywheel of the vehicle; this can also be one of the guide rings which is extended radially and which is fixed directly on the engine flywheel.
The input element, when it acts as a support disc for the friction liners, is backed on to one of the guide rings of the first damper, and is fixed to the latter by means of the spacers, or, in a modified version, by specific rivets.
The spacers extend through slots formed in the damper plate; in that case, the limitation of the angular displacement between the damper plate and the guide rings is obtained by cooperation of the spacers with the edge of the slots.
In another version, this limitation is obtained by interlocking of the turns of helical springs which constitute circumferentially acting resilient members, which are of high stiffness in this case, and which couple the guide rings and the damper plate elastically together.
The guide rings surround the output element of the damping device, which in general consists of a hub with internal splines; the same is true for the damper plate of the first damper, which meshes with the hub with a circumferential clearance. The first damper is accordingly directly acted on kinematically by the input element.
The pre-damper, or second damper, is disposed between the damper plate and one of the guide rings of the first damper, radially inwardly of the springs of the first damper.
The second damper is disposed, kinematically, directly upstream of the output element, and again comprises two guide rings disposed on either side of a damper plate, which is mounted on the hub, for rotation with the latter, by means of teeth. Resilient members, such as helical springs, couple the damper plate of the second damper to its associated guide rings; This damper plate of the second damper is seamed on to the hub, the splines of which have a different depth so as to define a shoulder which locates the said damper plate axially.
In such a device having two dampers, the guide rings of the second damper are coupled in rotation to the damper plate of the first damper.
The circumferentially acting springs of the second damper are less stiff than the circumferentially acting springs of the first damper. The second damper is adapted to absorb vibrations in the slow running mode of the engine, while the first damper is adapted to absorb vibrations in the normal travelling mode of the vehicle, or running mode.
The first and second dampers do give satisfaction, but in some cases problems arise.
For example, when, with a gear ratio engaged, the driver's foot is lifted on approaching a red light, the springs of the first damper are not well adapted to absorb the vibrations that occur in this mode; the same is true for the springs of the second damper, which are not stiff enough.
Another situation is also critical, namely driving in a line of traffic in traffic jams: the driver engages first gear and accelerates slightly, and here again the above mentioned dampers are not well adapted.
An object of the present invention is to overcome these drawbacks, and accordingly to optimise in a simple and inexpensive way the absorption of vibrations under all circumstances.